1. Field of the Invention
The present invention relates to a process for producing 2,2-dimethyl-1,3-propanediol mono(nydroxypivalate).
2,2-Dimethyl-1,3-propanediol mono(hydroxypivalate) 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxy propionate (hereinafter, simply referred to as DPHE) is a kind of ester-glycol having a neo structure. Owing to its molecular structure, it is characteristically excellent in heat resistance, weather resistance and hydrolysis resistance. Thus, it is watched with interest mainly as a starting material and modifier of polyesters, polyurethanes and polyacrylates and as a plasticizer or an lubricant.
2. Description of the Prior Art
DPHE is formed by a self-condensation reaction of hydroxypivaldehyde 2,2-dimethyl-3-hydroxypropanol (hereinafter, simply referred to as HPA) as expressed by the following reaction scheme: ##STR1##
As the prior process for producing DPHE by the self-condensation of HPA, the process mentioned in U.S. Pat. No. 3,057,911 which comprises heating HPA in the absence of catalyst is known.
However, the process which comprises simply heating HPA in the absence of catalyst is industrially impractical because the reaction progresses too slowly and by-products are formed in a large amount.
Thus, as its improvement, a number of processes which comprise carrying out the reaction in the presence of a catalyst have been proposed [for example, the processes using calcium hydroxide, barium hydroxide, strontium hydroxide and the like (Japanese Patent Publication No. 39,688/70, Japanese Patent Kokai (Laid-Open) No. 51,218/74); the processes using manganese catalyst (Japanese Patent Publication No. 41,888/71); the process using tertiary amine formate (Japanese Patent Publication No. 18,096/72); and the process using titanic ester or its polymer (Japanese Patent Publication No. 26,414/76)].
However, the catalysts proposed in the above-mentioned prior patents are disadvantageous in that they are unsatisfactory from the viewpoint of reaction velocity, some of them form a large amount of by-product, and some of them lose their catalyst activity when a slight quantity of water is present in the system. Further, some of these catalysts cause a coloration of reaction product or induce a thermal decomposition to lower the product yield to a great extent.